Iupati allowed a fumble-causing sack and another hit on Kaepernick in the first few series of the 49ers' 21-7 exhibition win Sunday over the San Diego Chargers.

Kaepernick didn't publicly chastise Iupati or other teammates after the game, dismissing his multiple hits as part of any game, though he said "of course" he encourages his linemen to prevent them. Iupati believes an "easy fix" to his technique will correct his pass-protection problems.

"It hurts because you always want to be on top of your game," said Iupati, a fifth-year veteran who's received Pro Bowl honors the past two seasons. "You learn from it and move on."

San Diego defensive tackle Corey Liuget beat Iupati for both hits on Kaepernick. Iupati will get a chance at redemption against Liuget when the Chargers return to Levi's Stadium on Dec. 20.

Overlooked through much of the offseason is how Iupati has recovered from a lower-leg fracture in last season's NFC Championship loss at Seattle. He did not need offseason surgery on that left leg, has been a full participant in practices and said it's improving daily.

"It'll be fine," Iupati said of his health.

The offensive line remains an issue for a couple of other reasons: Rookie center Marcus Martin suffered a left-knee injury Sunday that could sideline him two months, and right guard Alex Boone remains in a contract holdout that had no movement Monday, according to a source.

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But one aspect has stabilized on the line: Daniel Kilgore has secured the starting spot at center, a vacancy created by Jonathan Goodwin's free agency return to the New Orleans Saints.

Iupati praised Kilgore's intelligence and his ability to play low, and coach Jim Harbaugh noted that Kilgore has an ongoing streak without a bad snap.

"That's the last thing I want on my plate, a bad snap," Kilgore said.

Kilgore notes that he's ready for the starting role after being Goodwin's understudy the past three years. "The stats show I have not started, but I've been with the guys four years, and I feel comfortable with it," Kilgore said.

Wideout Stevie Johnson's roster spot is looking secure, even though he has only two receptions for 11 yards. Acquired in a draft-day trade with the Buffalo Bills, Johnson has "done an outstanding job," Harbaugh said. "I feel good about him being on the 53-man roster."

Joining Bowman (knee) on the reserve/physically-unable-to-perform list were tight end Garrett Celek (back) and defensive tackle Kaleb Ramsey (undisclosed). For the second straight year, Lattimore went on the reserve/non-football-injury list, where three rookies with knee injuries also were assigned: fullback Trey Millard, cornerback Keith Reaser and guard Brandon Thomas.